Spring clutch

ABSTRACT

A spring clutch is provided which can obtain stable engaging and idling functions. Torque transmitting surfaces of substantially the same diameter are formed on the inner periphery of a pulley hub mounted on a rotary shaft and that of a pulley. A coil spring pressed into both torque-transmitting surfaces is mounted so as to straddle both torque-transmitting surfaces. A chamfer is provided on the outer peripheral edge of an end face of the coil spring to stabilize the engaging and idling functions of the spring clutch.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a spring clutch for transmittingrotation of an input member to an output member and shutting off thetransmission of rotation from the output member to the input member.

[0002] Generally, in an automotive engine, since driving energy isproduced during the explosion stroke, the crankshaft is subjected tochange in the angular velocity in one rotation. When an engine accessoryhaving a large inertia such as an alternator is driven by such acrankshaft through a belt transmission, while the angular velocity ofthe crankshaft is dropping, if the rotating speed of the rotary shaft ofthe engine accessory exceeds it, slip occurs between a pulley mounted onthe rotary shaft and the belt.

[0003] Also, when the engine is changed over from high-speed tolow-speed and the moving speed of the belt drops, since the engineaccessory such as an alternator maintains high-speed rotation due toinertia, slip occurs between the pulley and the belt. During the slip,abnormal noise is produced or the belt wears and the durability lowers.

[0004] In order to solve such a trouble, in a clutch pulley devicedisclosed in JP patent publication 9-119509, a spring clutch is providedbetween a pulley hub mounted on the rotary shaft of an alternator and apulley mounted so as to be rotatable relative to the pulley hub totransmit the rotation of the pulley, which rotates by contact with thebelt, from the pulley hub to the rotary shaft through the spring clutch.When the rotating speed of the rotary shaft exceeds that of the pulley,transmission of rotation from the rotary shaft to the pulley is shut offby the spring clutch.

[0005] The spring clutch is formed with cylindrical surfaces having thesame inner diameter on the inner peripheries of the pulley hub and thepulley, and a coil spring having a larger outer diameter than thediameter of the cylindrical surfaces is mounted so as to straddle thecylindrical surfaces of the pulley hub and pulley such that as thepulley rotates, the diameter of the coil spring increases, therebyincreasing frictional force of the coil spring on the cylindricalsurfaces so as to transmit the rotation of the pulley to the pulley hubthrough the coil spring.

[0006] Also, when the rotating speed of the pulley hub exceeds that ofthe pulley, the coil spring is wound to weaken its frictional forceagainst the cylindrical surfaces, thereby causing slip between thecylindrical surfaces and the coil spring.

[0007] With such a coil spring, if an existing coil spring is used asthe coil spring, since the end faces of the coil spring are formed byshearing, there are burrs formed on the end faces in many cases.

[0008] If a coil spring having burrs formed on the end faces is mountedbetween the cylindrical surfaces of the pulley hub and the pulley, theburrs will engage the cylindrical surfaces, thus making unstable theengagement between the outer periphery of the coil spring and thecylindrical surfaces. Also, since it cannot slide smoothly on thecylindrical surfaces during shut-off of transmission of the reverseinput torque resulting from shrinkage of the coil spring, the springclutch cannot perform engaging and idling functions stably.

[0009] Also, since at the contact portions between the cylindricalsurfaces and the burrs, the surface pressure increases, the cylindricalsurfaces will be abraded abnormally.

[0010] An object of this invention is to provide a spring clutch whichcan perform stable engaging and idling functions and which can suppressabnormal wear of torque-transmitting surfaces against which the coilspring is pressed.

SUMMARY OF THE INVENTION

[0011] According to this invention, there is provided a spring clutchcomprising an input member, an output member mounted coaxially with theinput member, the input member and the output member being formed with acylindrical torque-transmitting surface, said surfaces havingsubstantially the same diameter, and a coil spring mounted to be pressedagainst the torque-transmitting surfaces so as to straddle thetorque-transmitting surfaces, wherein a chamfer is provided on the edgeof at least one side of the end faces of the coil spring that faces thetorque-transmitting surfaces.

[0012] The chamfer may be of a shape formed by grinding an edge in astraight line or arcuately, or by rounding an edge e.g. by tumbling, notby cutting.

[0013] By providing a chamfer on an end face formed by cutting the coilspring, it is possible to prevent the edge of the end face of the coilspring from being brought into strong frictional engagement with thecylindrical surfaces.

[0014] Thus, in a spring clutch in which cylindrical torque-transmittingsurfaces are formed on the inner peripheries of the input member andoutput member and a coil spring is mounted so as to straddle thesetorque-transmitting surfaces, when the diameter of the coil springincreases, the entire periphery of the coil spring is brought intofrictional engagement with the cylindrical surfaces. Stable engagingfunction is obtained and during idling due to reduction in diameter ofthe coil spring, abnormal wear of the torque-transmitting surfaces isavoided.

[0015] The spring clutch is not limited to one in which cylindricaltorque-transmitting surfaces are formed on the inner peripheries of theinput member and the output member.

[0016] For example, the spring clutch may be one in which cylindricaltorque-transmitting surfaces of substantially the same diameter areformed on the outer peripheries of the input member and the outputmember, and a coil spring is pressed onto these torque-transmittingsurfaces. In such a spring clutch, rotation of the input member istransmitted to the output member by reducing the diameter of the coilspring, and when the rotating speed of the output member exceeds that ofthe input member, the diameter of the coil spring is increased toprevent the rotation of the output member from being transmitted to theinput member.

[0017] The coil spring may be made from wire material having a circularsection. With a coil spring made from a wire material of a squaresection, during torque transmission by frictional engagement of the coilspring, since the entire outer or inner peripheral surface of the coilspring contacts the torque-transmitting surfaces, it is possible toobtain a spring clutch having a large load capacity and lower the wearof the torque-transmitting surfaces because the surface pressure is lowcompared to a coil spring made from a wire material of a circularsection.

[0018] With a coil spring made from a square wire material, its diameterincreases or decreases with the adjacent coil portions of the coilspring in close contact with each other, and while the diameter isincreasing or decreasing, the coil spring is deformed while twisting.Smooth twisting deformation is not possible because four corners of thesection of the wire material are deformed while abrading sides of theadjacent coil portions.

[0019] Thus, in the case of a coil spring made from a square wirematerial, chamfers are preferably provided on four corners of thesection of the wire material.

[0020] Other features and objects of the present invention will becomeapparent from the following description made with reference to theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a vertical sectional front view showing an embodiment ofthe spring clutch according to this invention;

[0022]FIG. 2 is an enlarged sectional view of a coil spring in theassembled state;

[0023] FIGS. 3A-3C are perspective views of examples of the coil spring;and

[0024] FIGS. 4(I)a to 4(III)c are front views showing examples ofshearing of coil springs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] Hereinbelow, a preferred embodiment of this invention will bedescribed with reference to the drawings. FIG. 1 shows a one-wayoverrunning clutch pulley device (hereinafter referred to as clutchpulley device) in which the spring clutch according to this invention isused. This clutch pulley device includes a rotary shaft 1. To one end ofthe rotary shaft 1, a pulley hub 2 as an output member is mounted. Apulley 4 as an input member is rotatably supported by a bearing 3mounted on the pulley hub 2.

[0026] The pulley hub 2 is prevented from rotating relative to therotary shaft 1 so as to rotate together with the rotary shaft. At oneend of the pulley hub 2, a flange 5 is formed and a cylindrical portion6 is provided on the outer periphery of the flange 5. On the innerperiphery of the cylindrical portion 6, a cylindricaltorque-transmitting surface 7 is formed.

[0027] The pulley 4 is rotated by the movement of an unillustratedribbed belt trained on its outer periphery. On the inner periphery ofthe outer end of the pulley 4, a cylindrical torque-transmitting surface8 is formed. The surface 8 formed on the pulley 4 is axially alignedwith the torque-transmitting surface 7. The inner diameters of thesetorque-transmitting surfaces 7, 8 are substantially equal to each other.

[0028] A coil spring 9 is mounted so as to straddle thesetorque-transmitting surfaces 7, 8. The outer diameter of the coil spring9 in its natural state is larger than the inner diameter of thetorque-transmitting surfaces 7, 8, and it is pressed into the pulley 4and the cylindrical portion 6 by shrinking it, so that its outerperiphery is frictionally pressed against the torque-transmittingsurfaces 7, 8.

[0029] If the pulley 4 is rotated rightwardly as viewed from theleft-hand side in FIG. 1, a right-hand coil spring is used as the coilspring 9, and if rotated leftwardly, a left-hand coil spring is used.

[0030] With the pulley clutch device having the abovesaid structure,when the pulley 4 rotates by contact with the belt, due to frictionalcontact with the torque-transmitting surface 8, the effective diameterof the coil spring 9 will increase, so that its press-engaging forceagainst the torque-transmitting surfaces 7, 8 increases until therotation of the pulley 4 is transmitted through the coil spring 9 to thepulley hub 2 and the rotary shaft 1 rotates in the same direction as thepulley 4.

[0031] While the rotary shaft 1 is rotating, if its rotating speedexceeds that of the pulley 4, the diameter of the coil spring 9decreases due to contact with the torque-transmitting surface 7 formedon the pulley hub 2, so that the frictional engagement force between thecoil spring 9 and the torque-transmitting surfaces 7, 8 decreases, slipoccurs at the contact portions between the coil spring 9 and thetorque-transmitting surfaces 7, 8, and the rotation of the rotary shaft1 is prevented from being transmitted to the pulley 4.

[0032] In this pulley clutch device, if there are burrs formed on theend face 9 a of the coil spring 9 by cutting, as described in thesection of problems the invention intends to solve, the burrs willengage the torque-transmitting surfaces 7, 8, which are cylindricalsurfaces, thus making unstable the frictional engagement force betweenthe the outer periphery of the coil spring 9 and the torque-transmittingsurfaces 7, 8. Also, because the coil spring 9 cannot slide smoothly onthe torque-transmitting surfaces 7, 8 while transmission of the reverseinput torque is prevented due to reduced diameter of the coil spring 9,the spring clutch cannot perform stable engaging and idling functions.

[0033] In order to solve such a trouble, as shown in FIGS. 2 and 3A, achamfer 10 is provided on the outer periphery of the end face 9 a formedby shearing a coil spring 9 made from a wire material having a circularsection.

[0034] By providing the chamfer 10 on the end face 9 a formed byshearing the coil spring 9, burrs formed during shearing are completelyremoved. Thus, when the diameter of the coil spring 9 is increased, theentire outer periphery of the coil spring is brought into frictionalengagement with the torque-transmitting surfaces 7, 8, so that stableengaging function is obtainable.

[0035] Also, during idling due to reduced diameter of the coil spring 9,the coil spring will slide smoothly on the torque-transmitting surfaces7, 8, thus preventing the torque-transmitting surfaces from getting wornabnormally.

[0036] In the example shown in FIG. 2, as the coil spring 9, a coilspring made from a wire material having a circular section is shown. Butas shown in FIG. 3B, the coil spring 9 may be one made from a wirematerial having a square section. In this case, a chamfer 10 may beprovided on all the sides of the outer peripheral edge of the square endface 9a, or chamfers 10 are provided only on edges facing thetorque-transmitting surfaces 7, 8.

[0037] If the coil spring 9 is made from a wire material having a squaresection, since the entire outer peripheral surface of the coil spring 9is brought into contact with the torque-transmitting surfaces 7, 8during torque transmission by the frictional engagement of the coilspring 9, a spring clutch having a large load capacity is provided.Also, since the surface pressure for the torque-transmitting surfaces 7,8 is low compared with a coil spring made from a wire material having acircular section, it is possible to reduce the wear of thetorque-transmitting surfaces 7, 8.

[0038] Twisting deformation develops in the coil spring 9 duringincrease or decrease in its diameter. Thus, with a coil spring 9 madefrom a wire material having a square section, since there are edges atthe four corners in the section of the wire material, it is deformedwhile the edges abrade sides of the adjacent coil portions, so thatsmooth twisting deformation is impossible.

[0039] As shown in FIG. 3C, by providing chamfers 11 at four ridges ofthe square wire material, smooth twisting deformation of the coil spring9 is possible.

[0040] For the coil spring 9, one with a predetermined length is formedby shearing. During shearing, if the wire material is soft and the coilspring 9 is sheared by radially moving the cutter 20 from theouter-diameter side toward inner-diameter side of the coil spring 9 asshown in FIG. 4(I)A, sagging b is formed on the outer-diameter edge ofthe sheared surface a and burr c is formed on its inner-diameter side,as shown in FIG. 4(I)C.

[0041] Since the sagging b provides a similar result to the case inwhich the chamfer 10 is formed, it eliminates the need of chamferingafter shearing.

[0042] In the mounted state of FIG. 1, the coil spring 9 has its outerperiphery functioning as a frictional engaging surface for thetorque-transmitting surfaces 7, 8, so that the burr c formed on theinner-diameter side of the sheared surface a will have no influence onthe transmission and shut-off of the turning torque. Thus, the burr cmay be removed or left as it is.

[0043] If the inner-diameter surface of the coil spring 9 is used as africtional engagement surface, the coil spring 9 is sheared by movingthe cutter 20 from its inner-diameter side to outer-diameter side.

[0044] In shearing a coil spring 9 made of a hard wire material, asshown in FIGS. 4(II)a and 4(II)b, because sagging is scarcely formed onthe shearing surface a, a chamfer 10 is formed after shearing on theouter-diameter edge of the sheared surface a as shown in FIG. 4(II)c.

[0045] As shown in FIGS. 4(III)a and 4(III)b, by obliquely shearing thecoil spring 9 with the cutter 20, the sheared surface a is made as aninclined surface. In this case, it is unnecessary to form a chamfer onone of the end faces 9 a of the coil spring 9, and a chamfer 10 isformed only on the other end face 9 a of the coil spring, as shown inFIG. 4(III)c.

[0046] In the embodiment, the spring clutch according to this inventionis applied to a one-way overrunning clutch pulley device. But it canalso be applied to a one-way flexible coupling described in JP patentpublication 11-218151.

[0047] According to this invention, by providing a chamfer on the outerperipheral edge of an end face of the coil spring, it is possible toobtain stable engaging and idling functions and also suppress abnormalwear of the torque-transmitting surfaces with which the coil spring isbrought into press engagement.

What is claimed is:
 1. A spring clutch comprising an input member, anoutput member mounted coaxially with said input member, said inputmember and said output member being formed with a cylindricaltorque-transmitting surface, said surfaces having substantially the samediameter, and a coil spring mounted to be pressed against saidtorque-transmitting surfaces so as to straddle said torque-transmittingsurfaces, wherein a chamfer is provided on the edge of at least one sideof the end faces of said coil spring that faces said torque-transmittingsurfaces.
 2. A spring clutch as claimed in claim 1 wherein said coilspring is made from a wire material having a circular section andchamfers are formed on the outer peripheral edges of both end faces ofsaid coil spring.
 3. A spring clutch as claimed in claim 1 wherein saidcoil spring is made from a wire material having a square section.
 4. Aspring clutch as claimed in claim 3 wherein chamfers are provided at allfour ridges of section of said coil spring.